Over the past several decades worldwide production, processing, storage, transportation and utilization of synthetic and naturally occurring chemical substances has led to the introduction of significant quantities of hazardous materials into the environment. Unintentional spillage of petroleum distillates, industrial solvents and other chemical substances has been caused, for example, by weathering, chemical corrosion and accidental damage to pipes, storage vessels, processing equipment, transportation vehicles, etc. Deliberate acts and carelessness have also contributed to the release of hazardous substances into the environment. The spillage of such materials has resulted in large numbers of polluted sites and enormous volumetric quantities of soil and groundwater which have been contaminated with hazardous substances. Soil contamination can cause extensive damage to the local ecosystem by accumulating in the tissue of animals and plants, and by causing death thereto and/or mutation to the progeny thereof. Such contamination can also present a serious health threat to humans, and, in extreme cases, can render the contaminated area unsuitable for human habitation. In many cases, contaminated sites can pose a danger to adjacent property, such as by entrainment of hazardous substances by local groundwater flow, and local laws frequently mandate remediation prior to the sale or lease of property wherein the soil has been contaminated with hazardous materials.
Various methods have been utilized for the treatment, remediation or disposal of contaminated soil. These methods generally include permanent removal of the contaminated soil to a secure landfill, incineration, indirect thermal treatment, aeration, venting, air sparging and bioremediation. Removal of contaminated soil to landfills is no longer an attractive alternative on account of the high excavation, transportation and disposal costs, and because of the potential for residual liability. Incineration and indirect thermal treatment can be achieved either on-site or off-site, but in either case involves excavation, handling and treatment of substantially all of the contaminated soil as well as significant amounts of soil adjacent to the contaminated soil. The soil must then either be transported to the treatment facility or else the treatment apparatus must be installed on-site. In either case, these methods generally involve enormous transportation and handling costs, and require large amounts of energy to combust or volatilize the contaminants. Other elaborate and expensive techniques which have been utilized involve excavation and treatment of the contaminated soil using multistep unit operations for separating and recovering the soil from the contaminants. Removal, incineration, indirect thermal treatment and other methods of handling contaminated soil which involve complete excavation of the contaminated soil have the advantage that they can be accomplished in a relatively short amount of time. These methods are particularly attractive in those situations where there is a substantial risk that the contamination will rapidly spread to adjacent property, however, in most cases such methods are prohibitively expensive.
Aeration, venting and air sparging are in situ techniques for removing volatile hazardous contaminants from the soil while simultaneously drawing oxygen into the contaminated soil to enhance biodegradation. Effective removal of hazardous materials by evaporation is generally limited to contaminants having a relatively high vapor pressure. In general, compounds such as polycyclic aromatic hydrocarbons, which have a low-vapor pressure, cannot be successfully removed by volatilization. Moreover, conventional bioremediation techniques utilizing indigenous microorganisms alone or in combination with naturally occurring or genetically altered exogenous microorganisms is not always effective for degrading certain types of recalcitrant contaminants, such as polycyclic aromatic hydrocarbons, which are strongly resistant to biodegradation on account of their polynuclear chemical structure and low concentration in the natural environment.
Thus, while various known techniques are available for the disposal or reclamation of contaminated soil, such methods do not generally provide a practical, affordable technology for remediating soil which has been contaminated with significant quantities of polycyclic aromatic hydrocarbons. Accordingly, there is a need for an inexpensive, environmentally acceptable method and means for remediating soil which has been contaminated with polycyclic aromatic hydrocarbons.